1. Field of the Invention:
The present invention is directed to a soldering apparatus having at least one stirrup electrode secured to a solder stirrup holder and heatable :;ith electrical resistance heat and having two solder webs lying opposite one another or four solder webs lying opposite one another in pairs whose work surfaces lie in one plane.
2. Description of the Prior Art
As an example, German application No. 31 49 236 generally discloses such a soldering device. The electrode holder of this known soldering device comprises small columns of conductive material electrically insulated from one another and between whose ends at least two stirrup electrodes are secured in interchangeable fashion. The U-shaped stirrup electrodes that can be heated by electrical resistance heating are manufactured of a planar plate composed of a resistor material such as tantalum or molybdenum and are attached in such a fashion that their work surfaces, lying on the urderside of the solder webs, come into contact with the elements to be soldered. Given a plurality of two or four stirrup electrodes, a total of four small columns are required for the electrode holders, these columns being arranged at a respective diagonal of the cross section of the soldering device and being mechanically connected to one another by a plurality of crcss-shaped bracings. For the power supply of four stirrup electrcdes, two small columns lying on a diagonal are connected to the cne pole of a power source, whereby the two other small columns are connected to the other pole of the power source.
German application No. 28 18 958 discloses another soldering device wherein the electrcde holder comprises two small columns of conductive material electrically insulated from one another and between whose ends a sirgle stirrup electrode is secured in an interchangeable manner. This stirrup electrode likewise has four soldering webs lying opposite one another in pairs whose working surfaces have the shape of a one-piece rectangular frame, whereby two soldering webs lying opposite one another are interchangeably secured to the allocated, small columns via upwardly-projecting continuations.
European application No. 011 046 discloses a further soldering device wherein a single stirrup electrode secured at an electrode holder has a total of four soldering webs lying opposite one another in pairs, whose working surfaces have the shape of a one-piece, rectangular frame. Here, however, each of the soldering webs has an upwardly projecting continuation allocated thereto which holds the scldering webs and serves as a power lead. Continuations that lie opposite one another thereby lie electrically parallel with one another.
The known soldering apparatus set forth above are particularly utilized for soldering electronic components having a large number of poles such as micropacs, flatpacks and the like to printed circuitboards, whereby the resistance heating of the stirrup electrodes is undertaken by current pulses. A reliable contact between the working surfaces of the stirrup electrodes, the terminal legs of the components and the interconnects or, respectively, terminal pads of the printed circuitboards must thereby be guaranteed both before the soldering process as well as over the entire duration of the soldering process. This requirement, however, cannot always be met in view of potentially-occurring arcings of the printed circuitboards, of tolerances of the printed circuitboards in the direction perpendicular to the plane of the printed circuitboards, of tolerances in layer thickness and of a possible skewed position of the printed circuitboards during the soldering process.